(CNN) -- They'd been looking forward to sharing a family meal of steak and lobster.

But something went terribly wrong after brothers Nehemiah and Brandon Fischer left their father's house last week. First, they got stuck in floodwaters during heavy rains south of Tulsa, Oklahoma. Then, highway patrol troopers came to help.

What happened next depends on who you ask.

This much is clear: Nehemiah Fischer -- a 35-year-old pastor -- is dead. Brandon Fischer, a restaurant owner, is behind bars on charges of assault and public intoxication. Authorities are investigating. And their father says a family in mourning is searching for answers.

"We're hearing one side of the story, which I believe is incorrect," father Martin Fischer told CNN on Monday. "All we want is the truth. We just want to know what happened."

Capt. Paul Timmons of the Oklahoma Highway Patrol told reporters Monday that the case remains under investigation and the troopers are on paid administrative leave. But he said they opened fire Friday night after Nehemiah Fischer assaulted a trooper, grabbing and shoving him to the ground.

A portion of a trooper dashcam video released at Monday's press conference shows the troopers, whose names have not been released, shouting at the men to move out of the rushing waters. Then, the men march toward them.

One trooper shouts: "Boys, state troopers, settle down, do you hear me?"

The shoving starts soon afterward. And the video shown at Monday's press conference ended with the image of a trooper pointing his gun in the direction of the struggle.

Speaking to CNN before troopers released the video Monday, Martin Fischer said something didn't add up in the story authorities were telling about the shooting.

"My sons are both law-abiding citizens. They would never, ever argue with a policeman," he said. "They have the utmost respect for the law."

Nehemiah had just gotten a pistol for his birthday and might have had it on his side, but never would have used it to harm someone, his father said.

"Nehemiah is an assistant pastor at the church and teaches. He's the real deal as far as the man of God," Martin Fischer said. "He takes his Bible and his Lord very serious."

Martin Fischer said his sons may have been taken by surprise and didn't realize bright lights they saw in the darkness were troopers coming to help them.

"A car pulled up shining their lights at them and yelling at them. They had no idea who it was," he said. "They just heard someone yelling at them."

But officials Monday stressed that the uniformed troopers had clearly identified themselves and worked to de-escalate the situation before they were assaulted.

Family members said later Monday that they hadn't seen the video and declined to comment.